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Abstract

Several well-established methods exist for recording and measuring the underlying signals of the brain; methods such as electrophysiology and fMRI, when taken together, have the capacity to disclose both local and global neuronal activity. Thus, we aimed to employ both techniques to construct a functional model of the insular cortex (IC), a recipient of afferents relaying information from the body’s viscera.
For our work, we performed a series of fMRI experiments in the anesthetized macaque (n = 11), where we measured the responses to interoceptive stimulation (e.g. lower gastrointestinal tract, cutaneous temperature, auricular vagus nerve branch, gustation); and exploited the gross functional anatomical localizations (area: 4mm2) of these functions to establish a foundation for subsequent electrophysiological sampling (area: 1mm2, n = 4) across the IC. Using these methods, our results reveal a topographic organization of interoceptive processing and highlight its functional similarity to that of the human insular cortex.
As localized by fMRI and electrophysiology, two anatomically discrete areas along the mid-anterior dorsal IC were responsive to oral and gustatory sensations. However, our fMRI results disclosed lower gastrointestinal activity to be predominantly correlated with the ventral anterior IC. Such results already depict a select arrangement of multi-modal inputs within the macaque insula. As the IC is the primary cortical recipient of interoceptive inputs, the manner in which this information is organized may disclose how these inputs are relayed to form a conscious percept of the body’s physiological state, contribute to emotional embodiment, and provide top-down influence on bodily function.